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Nanomaterials for Sustainable Waste Conversion, Energy Production, and Environmental Applications

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A special issue of Micro (ISSN 2673-8023). This special issue belongs to the section "Microscale Materials Science".

Deadline for manuscript submissions: 31 July 2026 | Viewed by 12143

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Dr. Constantinos Salmas

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Department of Material Science and Engineering, University of Ioannina, 45110 Ioannina, Greece
Interests: materials process engineering; porous materials; material characterization; kinetics; mesoporous materials; biomass and biowaste valorization; process engineering; gels as food packaging
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Prof. Dr. Michalis Karakassides

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Department of Materials Science and Engineering, University of Ioannina, 45110 Ioannina, Greece
Interests: catalysis; nanomaterials and nanotechnology; ceramic; composite and porous materials; oxide glasses; hybrid materials; mesoporous and phyllomorphic materials based on silicon or carbon; clay based materials; photocatalytic materials; magnetic oxide nanoparticles and zero valence iron; activated carbon materials produced from biomass; structure and physicochemical properties of materials with vibrational spectroscopic techniques; thermal analysis; porosimetry
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Dr. Nikolaos Chalmpes

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Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14850, USA
Interests: carbon layered materials; porous carbons; functionalization of carbon nanostructures; design, synthesis, and evaluation of nanomaterials towards the (electro) catalytic performance; activated carbon materials; nanoparticles; energy storage applications; Langmuir–Blodgett; electron microscopies; atomic force microscopy; graphene derivatives

Special Issue Information

Dear Colleagues,

Nowadays, the race for novel materials development is triggered by several modern applications such as the transition to electric vechicles, high-performance batteries, the replacement of chemical-based materials with bio-based biodegradable materials, etc. The advanced novel materials invented during the last few years have opened new research avenues for medical, energy, environmental, and several other applications. Materials for energy applications, activated carbon, and graphene, as well as active food packaging, food safety, reduced food waste, alternative food preservatives, biopolymers, medical building blocks, and even materials for space exploration and new planet habitation, could possibly originate from byproducts, biomass, and biowastes. Challenges such as the climate change effect, worldwide human hunger, the 9.5 billion global population in 2050, and natural resource limitations, have created new scientific fields for novel as well as innovative materials development. One of the dominant concepts to intensify the effort to solve crucial environmental and living problems on earth's life is the valorization of biomass and biowastes. Nanomaterials exhibiting unique physicochemical properties have emerged as a transformative class of materials. Current tests have indicated that they are highly effective in addressing global environmental and energy challenges. High surface area, tunable porosity, enhanced reactivity, and superior catalytic capacity are some of the advanced properties of these materials. Such properties indicate them as ideal candidates for sustainable waste conversion, energy production, and environmental remediation.

In waste management, energy production, and environmental applications, nanomaterials facilitate the efficient conversion of organic and inorganic waste into valuable products such as biofuels, hydrogen, value-added chemicals, advanced nanocatalysts with enhanced reaction kinetics and selectivity, next-generation energy storage and harvesting systems, etc.

Their application is extended in adsorption, photocatalysis, and membrane filtration for the degradation of organic pollutants, heavy metal removal, water purification, air quality improvement, and carbon capture, as well as in fuel cells, solar cells, batteries, and supercapacitors for improved energy efficiency, stability, and sustainability.

Their involvement in production processes leads to reduced-cost products with a neutral CO₂ balance in the production line.

The integration of nanomaterials into sustainable technologies paves the way for greener solutions to global challenges. However, ensuring their safe production, application, and disposal is crucial to minimizing potential environmental and health risks. Future advancements in nanomaterial design, functionalization, and scalability will further drive their role in achieving a more sustainable and cleaner world.

Dr. Constantinos Salmas
Prof. Dr. Michalis Karakassides
Dr. Nikolaos Chalmpes
Guest Editors

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Dr. Constantinos Salmas
Prof. Dr. Michalis Karakassides
Dr. Nikolaos Chalmpes
Guest Editors

Manuscript Submission Information

Keywords

nanomaterials
novel materials
innovative materials
biomass valorization
biomass conversion
waste management
waste valorization
waste conversion
materials engineering
materials science
materials for energy
materials for environment

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Published Papers (9 papers)

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Research

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19 pages, 2595 KB

Open AccessArticle

Hydrogen Evolution Kinetics on Noble-Metal-Lean Pd/Ag Nanowire Networks Supported on Graphite

by Martina Schwager, Niklas Käfer, Jenni Richter and Hannes Reggel

Micro 2026, 6(2), 30; https://doi.org/10.3390/micro6020030 - 30 Apr 2026

Viewed by 141

Abstract

The hydrogen evolution reaction (HER) plays a central role in electrochemical hydrogen production and requires catalysts that combine high activity with reduced noble metal usage. In this work, palladium nanoparticles (PdNPs) were deposited onto silver nanowire-modified graphite electrodes (Pd/AgNW/C) to investigate the influence of Pd loading on HER kinetics and catalytic efficiency. The electrodes were prepared by constant-current electrodeposition and characterized using polarization measurements and electrochemical impedance spectroscopy (EIS). The direct current (DC) results showed a pronounced enhancement of HER activity in the presence of Pd, while the highest mass-specific activity was observed at low Pd loadings. Increasing the Pd content further increased the overall current but reduced the catalytic efficiency when normalized to the Pd mass. EIS measurements revealed two contributions to the impedance response associated with processes occurring on different timescales. With increasing cathodic overpotential, both the charge transfer resistance and the low-frequency resistance decreased markedly, indicating accelerated reaction kinetics. The combined DC and alternating current (AC) analyses suggest that the silver nanowire network facilitates efficient electron transport and promotes a favorable dispersion of Pd nanoparticles at low loadings, enabling efficient HER catalysis with reduced noble metal usage. Full article

(This article belongs to the Special Issue Nanomaterials for Sustainable Waste Conversion, Energy Production, and Environmental Applications)

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21 pages, 4558 KB

Open AccessArticle

Rotational Triboelectric Energy Harvester Utilizing Date-Seed Waste as Tribopositive Layer

by Haider Jaafar Chilabi, Luqman Chuah Abdullah, Waleed Al-Ashtari, Azizan As’arry, Hanim Salleh and Eris E. Supeni

Micro 2026, 6(1), 3; https://doi.org/10.3390/micro6010003 - 5 Jan 2026

Viewed by 661

Abstract

The growing need for self-powered Internet of Things networks has raised interest in converting abundant waste into reliable energy harvesters despite long-standing material and technology challenges. As demand for environmentally friendly self-powered IoT devices continues to rise, attention toward green waste as an eco-friendly energy source has strengthened. However, its direct utilisation in high-performance energy harvesters remains a significant challenge. Driven by the growing need for renewable sources, the triboelectric nanogenerator has emerged as an innovative technology for converting mechanical energy into electricity. In this work, the design, fabrication, and characterisation of a rotating triboelectric energy harvester as a prototype device employing date seed waste as the tribopositive layer are presented. The date seeds particles, measuring 1.2 to 2 mm, were pulverised using a grinder, mixed with epoxy resin, and subsequently applied to the grating-disc structure. The coated surface was machined on a lathe to provide a smooth surface facing. The performance of the prototype was evaluated through a series of experiments to examine the effects of rotational speed, the number of grating-disc structures, the epoxy mixing process, and the prototype’s influence on the primary system, as well as to determine the optimal power output. An increase in rotational speed (RPM) enhanced power generation. Furthermore, increasing the number of gratings and pre-mixing of epoxy with the biomaterial resulted in enhanced output power. Additionally, with 10 gratings, operating at 1500 rpm, and a 24 h pre-mixing method, the harvester achieved maximum voltage and power outputs of 129 volts and 1183 μW at 7 MΩ. Full article

(This article belongs to the Special Issue Nanomaterials for Sustainable Waste Conversion, Energy Production, and Environmental Applications)

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25 pages, 5715 KB

Open AccessArticle

Exploring Structural and Electrical Behavior of Nanostructured Polypyrrole/Strontium Titanate Composites for CO₂ Sensor

by S. Mytreyi, Sharanappa Chapi, Sutar Rani Ananda, Nagaraj Nandihalli and M. V. Murugendrappa

Micro 2025, 5(4), 54; https://doi.org/10.3390/micro5040054 - 28 Nov 2025

Cited by 1 | Viewed by 697

Abstract

The current research presents the synthesis, characterization, and application of a novel gas sensor based on polypyrrole/strontium titanate (PPy/STO) nanocomposites for the selective detection of CO₂. Utilizing chemical oxidative polymerization, PPy and PPy/STO nanocomposites with varying STO (10–50) wt.% were synthesized and characterized. The structural and morphological analysis confirms the formation of spherical structure and well-dispersed PPy nanoparticles with increasing crystallinity and interaction of STO in PPy chain particle compactness as the STO content increases. The integration of perovskite STO within the conducting polymer matrix enhances the electronic structure, porosity, and surface area of the composite, promoting improved gas sensing performance. Electrical impedance spectroscopy reveals that the composites exhibit a frequency-dependent dielectric response and conduction attributed to charge carrier mobility and interfacial polarization effects. PPy/STO 20% exhibits highest conductivity and dielectric constants of 0.03604 Scm⁻¹ and 1.074 × 10⁴, respectively. Real-time CO₂ sensing experiments conducted at 50 °C demonstrate good sensitivity, stability, and rapid response/recovery characteristics, particularly for the PPy/STO 10% and 40% composites. These findings highlight the potential of PPy/STO nanocomposites as flexible, lightweight, and efficient materials for portable CO₂ gas sensors, addressing the growing needs for environmental and health monitoring. Full article

(This article belongs to the Special Issue Nanomaterials for Sustainable Waste Conversion, Energy Production, and Environmental Applications)

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24 pages, 4561 KB

Open AccessArticle

A Comparative Study on the Spinnability of Collagen/Pullulan Nanofibers Dissolved in Water as a Green Solvent Using Needle vs. Needle-Free Electrospinning Techniques

by Elçin Tören and Jakub Wiener

Micro 2025, 5(4), 52; https://doi.org/10.3390/micro5040052 - 23 Nov 2025

Cited by 2 | Viewed by 775

Abstract

This study investigates electrospinning methodologies using distilled water as an environmentally friendly and non-toxic solvent for fabricating nanofibers composed of fish collagen (COL) and pullulan (PUL). The underlying hypothesis is that incorporating PUL will enhance the spinnability of the electrospun solution through the formation of hydrogen bonds with COL, thereby facilitating improved fiber development within an aqueous system. This study examined the interactions between COL and PUL molecules, focusing on hydrogen bonding and the consequential alterations in secondary structural conformation, to elucidate their effects on the spinnability and stability of COL in water-based solutions. Furthermore, this study emphasizes the advantages of needle-free electrospinning, which enables the efficient production of nanofibers and offers scalability potential for industrial applications. The architecture and properties of the resultant ultra-thin COL/PUL fibers were comprehensively characterized, underscoring their suitability for various biomedical applications. The development of PUL-based skin nanofibers represents a significant advancement in the field of biomaterials, offering a biocompatible and biodegradable alternative for dermatological applications, including skin regeneration, wound healing, drug delivery, tissue engineering, and cosmetic science. The benefits of needle-free electrospinning, such as enhanced production efficiency and scalability, are particularly emphasized, demonstrating its potential for the large-scale commercial manufacturing of biocompatible nanofibers. This study aimed to address the research gap regarding the use of distilled water as an eco-friendly and safe solvent for electrospinning nanofibers made from collagen and pullulan. This study aimed to investigate the unexplored potential of distilled water for this application. Full article

(This article belongs to the Special Issue Nanomaterials for Sustainable Waste Conversion, Energy Production, and Environmental Applications)

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17 pages, 6575 KB

Open AccessArticle

Enhanced Energy Storage Properties in Lead-Free (1−x)(BNT–5BT)–xBCZT Ceramics: Comparative Study of Direct and Indirect Synthesis Routes

by Mauro Difeo, Leandro Ramajo and Miriam Castro

Micro 2025, 5(4), 51; https://doi.org/10.3390/micro5040051 - 16 Nov 2025

Viewed by 641

Abstract

This work presents a comparative study on the structural, microstructural, and functional properties of a novel lead-free solid solution based on (1−x)(0.95(Bi_0.5Na_0.5)TiO₃–0.05BaTiO₃)–x(0.5Ba_0.7Ca_0.3TiO₃–0.5BaTi_0.8Zr_0.2O₃), abbreviated as (1−x)(BNT–5BT)–xBCZT, with x values ranging from 0 to 0.20. Two different synthesis routes were evaluated: a direct route, where all raw materials were mixed and processed in a single step, and an indirect route, where BNT–5BT and BCZT were pre-synthesized separately and later combined. X-ray diffraction (XRD) and Raman spectroscopy confirmed the formation of single-phase perovskite structures, with progressively increasing tetragonality as x increased. Field-emission scanning electron microscopy (FE-SEM/EDS) revealed dense microstructures and secondary rod-like phases whose morphology and amount evolved with composition. Dielectric measurements indicated an enhanced relaxor behavior with increasing BCZT content, evidenced by a shift in the T_F–R with frequency. The direct route resulted in more efficient dopant incorporation, leading to stronger dielectric relaxation, reduced hysteresis losses, and improved energy storage performance. The maximum energy efficiency (η) reached 43.7% for x = 0.075 via the direct route, compared to 38.0% for the same composition prepared by the indirect route. The maximum recoverable energy density (W_rec) reached 0.42 J·cm⁻³ for x = 0.075 via the direct route (vs. 0.40 J·cm⁻³ for the indirect route), with corresponding peak energy efficiencies of 43.7% and 38.0%, respectively. These findings demonstrate that (1−x)(BNT–5BT)–xBCZT ceramics synthesized via the direct route constitute a promising and scalable approach for high-efficiency, lead-free dielectric capacitors. Full article

(This article belongs to the Special Issue Nanomaterials for Sustainable Waste Conversion, Energy Production, and Environmental Applications)

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14 pages, 6801 KB

Open AccessArticle

Effect of Zr Doping on BNT–5BT Lead-Free Ceramics: Substitutional and Excess Incorporation Analysis

by Mauro Difeo, Miriam Castro and Leandro Ramajo

Micro 2025, 5(3), 35; https://doi.org/10.3390/micro5030035 - 28 Jul 2025

Cited by 1 | Viewed by 1087

Abstract

This study evaluates the effect of zirconium (Zr) incorporation on the structural, microstructural, and functional properties of lead-free ceramics based on the 0.95(Bi_0.5Na_0.5)TiO₃–0.05BaTiO₃ (BNT–5BT) system. Two distinct doping strategies were investigated: (i) the substitutional incorporation of Zr⁴⁺ at the Ti⁴⁺ site (BNT–5BT–xZr_sub), and (ii) the addition of ZrO₂ in excess (BNT–5BT–xZr_exc). The samples were synthesized via conventional solid-state reaction and characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM/EDS), and electrical measurements, including dielectric, ferroelectric, and piezoelectric responses. Both doping routes were found to influence phase stability and electromechanical performance. Substitutional doping notably reduced the coercive field while preserving high remanent polarization, resulting in an enhanced piezoelectric coefficient (d₃₃). These results highlight the potential of Zr-modified BNT–5BT ceramics for lead-free energy harvesting applications. Full article

(This article belongs to the Special Issue Nanomaterials for Sustainable Waste Conversion, Energy Production, and Environmental Applications)

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14 pages, 4290 KB

Open AccessArticle

Multifunctional Green-Synthesized Cu₂O-Cu(OH)₂ Nanocomposites Grown on Cu Microfibers for Water Treatment Applications

by Hala Al-Jawhari, Nuha A. Alhebshi, Roaa Sait, Reem Altuwirqi, Laila Alrehaili, Noorah Al-Ahmadi and Nihal Elbialy

Micro 2025, 5(3), 33; https://doi.org/10.3390/micro5030033 - 5 Jul 2025

Viewed by 1270

Abstract

Free-standing copper oxide (Cu₂O)-copper hydroxide (Cu(OH)₂) nanocomposites with enhanced catalytic and antibacterial functionalities were synthesized on copper mesh using a green method based on spinach leaf extract and glycerol. EDX, SEM, and TEM analyses confirmed the chemical composition and morphology. The resulting Cu2O-Cu(OH)₂@Cu mesh exhibited notable hydrophobicity, achieving a contact angle of 137.5° ± 0.6, and demonstrated the ability to separate thick oils, such as HD-40 engine oil, from water with a 90% separation efficiency. Concurrently, its photocatalytic performance was evaluated by the degradation of methylene blue (MB) under a weak light intensity of 5 mW/cm², achieving 85.5% degradation within 30 min. Although its application as a functional membrane in water treatment may raise safety concerns, the mesh showed significant antibacterial activity against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria under both dark and light conditions. Using the disk diffusion method, strong bacterial inhibition was observed after 24 h of exposure in the dark. Upon visible light irradiation, bactericidal efficiency was further enhanced—by 17% for S. aureus and 2% for E. coli. These findings highlight the potential of the Cu₂O-Cu(OH)₂@Cu microfibers as a multifunctional membrane for industrial wastewater treatment, capable of simultaneously removing oil, degrading organic dyes, and inactivating pathogenic bacteria through photo-assisted processes. Full article

(This article belongs to the Special Issue Nanomaterials for Sustainable Waste Conversion, Energy Production, and Environmental Applications)

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18 pages, 3043 KB

Open AccessArticle

Fe-Doped ZnS Quantum Dot Photocatalysts for the Degradation of Cefalexin in Water

by Sonia J. Bailon-Ruiz, Yarilyn Cedeño-Mattei and Luis Alamo-Nole

Micro 2025, 5(3), 31; https://doi.org/10.3390/micro5030031 - 22 Jun 2025

Cited by 5 | Viewed by 1852

Abstract

This study reports the synthesis, structural characterization, adsorption studies, nanoscale interaction, and photocatalytic application of pure and Fe-doped ZnS quantum dots for the degradation of the antibiotic cefalexin in aqueous solution. Nanoparticles were synthesized via the microwave-assisted method, and Fe doping was introduced at a 1% molar ratio. HRTEM images confirmed quasi-spherical morphology and high crystallinity, with particle sizes averaging 2.4 nm (pure) and 3.5 nm (doped). XRD analysis showed a consistent cubic ZnS structure. UV-vis spectra showed strong absorption at 316 nm for both samples, and PL measurements revealed emission quenching upon Fe doping. Photocatalytic tests under UV light demonstrated significantly higher degradation rates of 10 ppm cefalexin with Fe-doped ZnS, reaching near-complete removal within 90 min. Adsorption experiments revealed higher affinity and adsorption capacity of Fe-doped ZnS toward cefalexin compared to pure ZnS, as demonstrated by the Freundlich isotherm analyses, contributing significantly to enhanced photocatalytic degradation performance. High-resolution QTOF LC-MS analysis confirmed the breakdown of the β-lactam and thiazolidine rings of cefalexin and the formation of low-mass degradation products, including fragments at m/z 122.0371, 116.0937, and 318.2241. These findings provide strong evidence for the structural destruction of the antibiotic and validate the enhanced photocatalytic performance of Fe-doped ZnS. Full article

(This article belongs to the Special Issue Nanomaterials for Sustainable Waste Conversion, Energy Production, and Environmental Applications)

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Review

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34 pages, 1018 KB

Open AccessReview

Properties and Preparation of Alumina Nanomaterials and Their Application in Catalysis

by Hairuo Zhu, Kangyu Liu, Zhaorui Meng, Huanhuan Wang and Yuming Li

Micro 2025, 5(3), 38; https://doi.org/10.3390/micro5030038 - 12 Aug 2025

Cited by 2 | Viewed by 4200

Abstract

Nanomaterials are materials in which at least one dimension in three-dimensional space is at the nanoscale. In recent years, nano-alumina has attracted much attention due to its large specific surface area and pore volume, as well as novel optical, magnetic, electronic, and catalytic properties. This review summarizes the preparation methods of nano-alumina based on the basic phases and properties of alumina materials, focusing on one-dimensional, two-dimensional, and three-dimensional nano-alumina preparation methods, which can provide some theoretical guidance for the subsequent development of efficient nano-alumina materials. Finally, the application of nano-alumina materials in catalysis is reviewed, and some suggestions are provided for improving the use of nano-alumina in the catalysis field. Full article

(This article belongs to the Special Issue Nanomaterials for Sustainable Waste Conversion, Energy Production, and Environmental Applications)

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